Liquid crystal devices

ABSTRACT

Liquid crystal devices, an operation state of which is dependent upon substantially unidirectional liquid crystal orientation, includes a contacting surface which has parallel grooves or ridges. Liquid crystal orientation is attributed to minimization of elastic energy.

United StatesPatent n91 Berreman et al.

[ Jan. 22, 1974 LIQUID CRYSTAL DEVICES Inventors: Dwight Winton Berreman,

Westfield; Saul Meiboom, Berkeley Heights; Donald Lawrence White, Bernardsville; Frederic Jay Kahn, Stirling, all of NJ.

Bell Telephone Laboratories, Incorporated, Murray Hill, NJ.

Filed: June 23, 1972 Appl. No.1 265,459

Assignee:

us. Cl 350/160 LC 350/i50 Int. Cl. oozr 1/16 Field of Search "350/160 LC,

References Cited UNITED STATES PATENTS l0/l972 Cartmell et al. 350/150 Wyrenne et al. 350/ Lc Heilmeier et al. 350/160 LC Primary ExaminerEdward S. Bauer Attorney, Agent, or FirmW. L. Keefauver et al.

I 57] ABSTRACT Liquid crystal devices, an operation state of which is dependent upon substantially unidirectional liquid crystal orientation, includes a contacting surface which has parallel grooves or ridges. Liquid crystal orientation is attributed to minimization of elastic energy.

21 Claims, 6 Drawing Figures PArEu-Igmmzzmza satnanrz F/G. 4A

TRANSPARENT ELECTRODE LIQUID CRYSTAL TRANSPARENT ELECTRODE MIRROR 1 LIQUID CRYSTAL Devices BACKGROUND OF THE INVENTION 1. Field of the Invention The invention is concerned- There has been a growing interest, both scientific and technological, in the unusual class of liquid materials which evidence varying degrees of crystalline order.

These materials have been known for'some time, see G. W. Gray Molecular Structure and Properties of Liquid Crystals, Academic Press, 1962. Liquid crystals are traditionally considered to fall into any of three classes: nematic (directional but not positional ordering with molecules generally aligned unidirectionally in nonlayered fashion throughout the bulk of at least a portion of the liquid), cholesteric (in which molecular alignment is essentially like the nematic variety locally (and considered a species of nematics) but in which succeeding molecules rotate so as to result in helical alignment), and smeetic (in which there is some degree of layered ordering). n

A review articleat page 20 in Electra-Optic Systems Design, February I972, describes a number of device applications for liquid crystals. Devices described may serve a number of functions, e.g., memory, switching, polarizing, polarization detecting, modulation, as a controllable dichroic element, display, etc.

Display devices are exemplary. and, at least at the present time, it would appear that it is primarily in this area that attention is focused. As compared with competing devices, liquid crystal devices generally require lower power level for switching between the operating states (to produce changes in transmission, scattering, reflection, etc.)..A distinct further energy saving results from the fact that they may utilize ambient lighting. Power requirements for certain types of liquid crystal displays are small. Typical operating power requirements are of the order of 1/100 of that required for displays including light sources.

Liquid crystal devices fall into a variety of categories. ln general, a characteristic in common with most such devices is that readout is optical. ln general, information, regardless of type; whether transitory or permanent; whether binary or analog; whether numerical or pictorial; whether reflective or transmissive; involves some change in ordering.

The most common type of device at this time involves "dynamic scattering". in accordance with this mechanism, the unenergized liquid crystalline medium is aligned and so is essentially transparent to light. A change in ordering is produced by an actual passage of ionic current through the medium so as .toproduce a degree of turbidity thereby converting the medium gen-- .2 I namic scattering device. This latter effect is sometimes designated fast turn-off mode". Response times havebeen reported as less than 5 milliseconds as compared with 100 to 200 milliseconds for the more common dynamic scattering.

Both dynamic scattering and turn-off mode devices are ordinarily transitory in the sense that the effectof the turbidity disappears when the energy source is turned off. A permanent memory results if some cholesteric material is included with the usual nematic phase. The twist introduced by the cholesteric fraction tends to lock the medium. Erasure may naturally occur over a long term or may be'accomplished by temperature increase. Erasure can be induced'by application of nied by a change in optical properties of one form or another. Change may involve disordering (resulting from heating the nematic (or cholesteric) phase) in the manner ,of the dynamic scattering device described above or as a change in ordering as between liquid phases sometimes with the assistance of polarizers which may produce a change, for example, in opacity, color,

etc.

- A significant class of devices yet to be developed to a level of commercial feasibility depend on field effect rather than actual current flow. Such devices, which may utilize oneor more transparent electrodes, again, generally involve a medium which is oriented before being energized. The effect of the field is to produce disorder or sometimes a change in order. The latter may utilize crossed polarizers where both ordering directions are transversed to the interrogation direction or may depend on a change in transparency where one of the ordering directions is parallel to the viewing direction. Field-effect devices utilizing cholesteric materials may depend on color changes (with color generally being introduced or enhanced when the order is such that the helical axis is parallel to the interrogation direction). Devices may depend on a variation in a number of optical properties, e.g., absorption. scattering, diffraction, refraction.

A number of reasons exist for utilizing mixed media.

' Mixtures of nematic phase materials (and nematic is erally to a milky white or opaque appearance. Energi- I zation may be do. or a.c. with some preference for the latter in terms of increased lifetime for the device. At certain critically high frequencies using a.c. energizing,

response time is shortened due to oscillating domains instead of the turbidity which occursin the usual dyhereafter used in the generic sense in this description as including cholesteric) may be to change and/or increase initiation or range of temperature in which this phase is stable. Nematic phase material exhibiting no cholesteric ordering may be modified by inclusion of small amounts of cholesteric variant to bring about perman'ency of the imposed signal. Solvent-solute systems are sometimes necessary where it is desired to utilize material which, in the pure form, transforms directly from solid to disordered liquid, Color may be introduced by inclusion of dyestuff which aligns with the nematic phase material so as to enhance the dichroism inherent in this phase or so as otherwise to change color on undergoing transition between ordered and disordered states. This latter has been referred to as guesthost interaction effect. Any of the classes of devices discussed above may operate by reflection or transmission. Reflection may make use of a back mirror whereas transmissive effects best utilize sandwiching transparent elements.

Most devices described in the literature utilize electro-optic effects (either conductive or field effect) or thermal effects. Other devices-may depend upon the For example, shortlifetime may be attributed to interaction of certain types of liquid crystals with certain types ofsubstrate materials. Also, stability of such substrate materials is sometimes poor with deterioration resulting from such ambient conditions as humidity, high temperature, ultraviolet light, ozone, etc.

SUMlvlARY OF THE INVENTION In accordance with the invention, alignment of liquid crystals of any of the types described in the preceding section for use in any devices, including those also described in that section, is accomplished on a class of substrates generally incapable of producing such alignment by Van der Waals forces. In general, such alignfield, for example, required to induce any of the changes described, may result only at the intersection of two axial directions, each of which is responsible for i for.

imposing less than the requisite amount of energy producing the change.

Devices have thus far been described primarily in a change of state. Workers'have, however, not over- 7 looked the possibility of utilizing ordinarily liquid crystals as simple polarizers. In such use, many of the nematic materials particularly when admixed with guest dyestuff exhibit extinction ratios comparable to competing polarizing materials. The cholesteric' variant is optically active and is sensitive to the sense of circular polarization of an incident beam. Devices based on this latter effect have been proposed.

For the most part, all devices described depend upon at least one operating state corresponding with substantial alignment. Others, while not requiring such alignment, may show enhanced contrast where alignment is achieved. Accordingly, workers have sought out and developed a number of techniques for influencing orientation.' It has been generally assumed that orientation of any'of the liquid crystal phases is dependent upon Van der Waals forces. operating. on a molecular level. Accordingly, use hasbeen made of substrate'materials which, themselves, consists of long chain linear molecules aligned in the desired direction. Examples of such materials are linear hydrocarbon polymers, such as high density polyethylene, and other materials having little branching. Where use has been made ofsubstrates of other materials, as, for example, silicate glass and the like, a variety of treatments have been used to alter the surface so as to accomplish the desired alignment. One

' strate material must be of, or include, materials of the requisite molecular variety. Many of the deficiencies noted in devices thus far may be attributed to this restriction in substrate material.

ment results from minimization of elastic energy in the 1 body of the liquid crystal. Alignment results when use is madeof a substrate having ridges or grooves of dimensions and spacings of the order of tens of angstrom units or greater. Such grooves or ridges may be produced on an inorganic or organic media totally lacking in the characteristics required for the traditional mechanism utilizing Van der Waals forces. Such substrate surfaces may be produced in a variety of manners as by mechanical scoring, casting, etching, photolithography,

ion bombardment, etc. Substrate may be totally amorphous, may be polycrystalline, or even crystalline. In

the latter, surfaces may be modified with ridges running in a direction different from that which would otherwise be induced by virtue of any influence resulting from the crystallographic lattice itself.

Devices constructed in accordance with the invention may exhibit certain operational advantages over prior art devices. lmp'roved lifetime, for example, may arise simply by reason of the broader class of substrate material now made available. Similarly; longer lifetime may result by elimination or at least lack of dependence on orienting linear long chain molecules which may react with liquid crystals or other media or which may deteriorate due to any of a variety of mechanisms (e.g., reaction between liquid crystal and substrate oxidation of substrate, etc.).

As in relevant prior art devices, there is oftentimes the requirement that liquid crystals be aligned with a major axis parallel to a substrate surface. Under certain circumstances, where the wetting angle is large, such alignment may be accomplished or improved by utilizing an intermediate layer of any of the class of materials known as surfactants. The effect of such material is to increase the wettability of the substrate surface for the liquid crystal.

Alternatively, the prior art has made use of surfactants which induce alignment in adirection orthogonal to the direction of the surface. Such materials, which decrease wetting angle or show an affinity for a specilied end portion of a liquid crystal, have been utilized in the fabrication of devices in which an operating state utilizes this type of orientation. Such surfactants may find use in devices constructed in accordance with the.

invention where a second operating state involves alignment parallel to a substrate surface. In such event, however, alignment, at least :in part, induced by the ridges or grooves commongto all devices of the invention, is brought about by imposition of an external influence, such as an electric field.

Whereas devices of the invention depend upon alignment of liquid crystals due to surface undulations, cer tain device designs may be such that different alignment is desired in different localized regions. This is accomplished, inaccordance .with the invention, merely .by changing direction of ridges or grooves, accordingly.

BRIEF DESCRIPTION OF THE DRAWING DETAILED DESCRIPTION The Figures The arrangement of FIG. I- includes a liquid crystal layerl sandwiched between two electrodes 2 and 3, at least one of which is grooved so as to orient the liquid crystalline material of layer I. One or both electrodes 2 and 3- maybe transparent depending upon whether the device-is designed to operate by reflection or transmission. Electrodes 2 and 3 are optionally supported by layers 4 and 5 which are transparent or reflective in accordance with the intended operation of' the device shown. Either or both of layers 4 and 5 may be pro-.

vided with grooves which are replicated by electrodes 2 and 3 so as to finally influence alignment of layer I or layers 4 and 5 may be grooved. Elements 6 and 7, shown in phantom, are polarizers which may be crossed or not and which function to introduce or enhance contrast as between two operating states of FIG. I. Electrodes 2 and 3 are energized by electrical source 8 when switch 9 is closed. Electrical source 8 may function as a current source, in the instance of dynamic scattering devices, or, primarily, as a voltage source in the instance of field effect devices.

- The device of FIG. I may also be utilized as a simple polarizcr by appropriate choice of composition of material I and groove orientation of interface/s formed between layer 1 and 2 and/or 3. Polarization may result in the absence of energizing, in which event, electrical source 8 may be eliminated.

FIG. 2 depicted in the form ofa device of FIG. 1, represents a species of that device in that electrodes I2 polarization of light. Energization by electrical source- 18 upsets the order or, alternatively, reorders the crys tals with their major axes perpendicular to the plane surface. Unenergized, the 90 twist imposed on the alignment of the liquid crystal from electrode II to electrode 12 results in' transmissionthrough crossed polarizers I6 and I7. With a field imposed or with the crystal. Layer 3 1 is sandwiched by layers 32 and'33 which may both function as electrodes with current or voltage supplied by source not shown. Both electrodes 32 and 33 may be transparent or, for reflective operation, one, for example, 32, may be mirrored. In common with all devices depicted and described, alignment of the liquid crystal layer 31 is influenced by grooves or ridges which are parallel over at least a portion of one or both of the electrode surfaces forming interfaces with layer 31. Layers 34 and 35, which may serve as the actual substrate bodies, may be constructed of any of the materials described herein. Detailed requirements for the nature of materials contacting the liquid crystalline medium are described in the following section. Layer 36 is so designed asto selectively transmit some portion of light, depending upon the state of liquid stances, light is not transmitted (or reflected) in the unenergized state. With passage of current or application of voltage, layer3l is disordered or reordered. so as to permit transmission or reflection) of light energy of the appropriate polarization. The purpose of the dyestuff in such a cell is to increase absorption of the liquid crystal for the incident light so as to increase the polarization extinction ratio. I

FIGS. 4A, B, and C are an elevational view and electrode details, respectively, of a form of liquid crystal device of a coincident array design designed to operate as a numerical display. The device depicted consists of liquid crystal 4! sa ndwiching electrodes 42 and 43, supporting layers 44 and 45, and polarizers 46 and 47. Layer 48, shown in phantom, is a mirror which permits use of the depicted device in a reflective mode. Orientation of layer 4t, and functioning of all other elements depicted, is, as described in any of the figures above except for the detailed operation of electrodes 42 and 43.

electrode arrangement found sufficient for numerical display. Electrode 50 results in orientation within the region of crystalline material corresponding with seg-' ments 50a, 50b, 50c, etc. Electrode 51 similarly influences regions corresponding with segments 51a, 52a,

etc., and similarly denoted segments are influenced by remaining electrodes 52 through 56. Electrodes of electrode layer 43,-shown in detail 4C, two of which are designated 60 and 6l, define figure eights and are addressed sequentially at times corresponding with desired portions of electrode layer 42. Such a device may operate, for example, in the manner of the device of FIG. 2 with operation as there described. Disalignment or realignment results only in those portions of liquid crystal-layer4l sandwiched between energized segments of electrode layers 42 and.43. 'l 'he patterns depicted are in commercial use for numerical displays.

which may operate The device of FlG. 4A is representative of a family of coincident energy devices which may serve a variety of functions. as displays, either transmissive or reflective. A variety of electrode patterns operating coincidentally, either by passage of current or imposition of field, may result in a variety of symbols or designs of a which the patterns-of details 48 and 4Cv are exemplary.

Compositional Requirementsa. Substrate The term substrate in this section has reference to the composition of the surface actually in intimate contact with the liquid crystal. In this sense, this term may have a slightly different meaning from the term as utilized in the figure description. The significance of the substrate units. In general, preferred depth '(or height) of such current or field on the liquid crystalline material. All

such devices utilize straddling electrodes which, to

minimize electrical energy expenditure, are desirably in intimate contact with the liquid crystalline material. Since devices of concern generally operate at visible or near-visible light wavelengths, it is a requirement ofthis preferred class of devices that'such electrodes be trans I N= N-- and i l M- l arent to su hli ht. Surface'm. "l with the llquld F f goes p Electrode mate xials meeting the foregoing requirethe e lnvenuvc phllosphy' h mvemmll ls prerih ments include tin oxide 'variants such as indium-doped r r ijz l s gfi ga g i zg gi i gfa g g g i 3: 3: tin oxide, as well as very thin layers of elemental metg I y I g als. Reflective devices may utilize an electrode which primari yor so e y by Van der Waa s forces between is p q and Such y be cdmpoqed of y of the I l) in lin *ar substrate molecules on the one hand g F L I h usual metallic materials. Prior art devices, in which it mdJ'quld crysial q l f on e Other' The.esscnce was sought to produce alignment on such electrodes of the present invention is in alignment being induced accompfighed Um end -y use Ofa residue of g chain 's'n 'thn l lar' 1 crystal dlmen S l l ecu molecules such as cellulose residue produced by rub- -S' For purpfise of dfflleremlinmg the present m bing with lens paper. In accordance with the present vcnnonpver the pnor n Specified that the nature invention such electrode surfaces are desirably free of of the substrate, as defined in this'section, is such that Such residue but are provided with ridgeq or intermolecular forces between SubIqrate and hquld grooves responsible for alignment in accordance with. .Cryslal. c.annm re.sponslblc ahgnmem' Accord the invention. Such contour variations may be promgly n ls s'peclfiedm the negmwe that-the Surface of duced by transmission through very thin electrodes Such .qubstmte "l not be .composed of 'l of from underlying grooved or ridged support materials, sufficient length as to be orientable and/or so oriented or y y be produced dirccny in the electrode F 5 produce alignment Ofhqmd crystals' Accordmgly' The foregoing requirements are of course to be apdeslgnat'ed. s.uch Subswate meet the mqulrc' plied only to the region within which alignment is demfims of the i nlamfcst no long ralige sired. This may constitute the entirety of the liquid molecular ordering, by which is meant, an ordering cryqml region or ,1 portion thereof over the dimensions of IOOOangstrom units or greater. The Liquid Crystal Positive tcrmlnglogy is cxpedlcni in Canal" classes Liquid crystals suitable for the practice of the invenhubsfrate l l These mammals may be Prcfc i tion do not differ from those otherwise found desirable by virtue of Mammy? uansparellcy or other clldraqlens- 40 for device use. As indicated they may be smectic nemade avmlablc only vmuc of dlverilty of matic or as a species thereof cholesteric in some opmammals whlch may be uuhzed by following. the mvencrating state. They may be pure substances or they inay tive teaching. ln such terms, substrate materials may be I I h constitute any of the types of admixtures discussed truly il typlca g l er under the section entitled Description of the Prior z j m fi zz z i 2 5 g; Art". Chemical compositions found particularly useful a S p0 ymc y y y as nematic phase materials are generally of the form .polycrystalline or monocrystallinc. Such materials are v exemplified by tin oxide (acommonly used transparent W-mm electrode material) and quartz. A further requirement of such substrate surface, in accordance with the invenv tion, is the surface undulations (ridges-or grooves) which are themselves responsible for liquid crystal where h drk, d R d cemergrqups (R are alignment in whole or in part (in the unenergized or engiven i th f ll i tabl m--. TAgm.

Hi R2 R3 ciii0- ()II=N- "'CIID B cmcmo- CIi=-N- 0.iIv "lrans stllbeiiederivatlva CHiCHiO- -CI{=C CH CH(CII;)C41I Alkoxybenzyltdene amtnophenyl- CH;(CI-I1),,O CH=N- 0 acylate derlvatlves. 1|

O--C CH CH Cyano-Schlfl bases. N C- CH=N OC|II( 2) Merck NLC N4... 0110- 0 o -cim ergizcd condition). Surface ridges or grooves, to meet the inventive requirement; must represent a change in elevation from the surface plane of a minimum at least from a practical standpoint ofthe order of i0 angstrom The invention is premised on alignment due to minimization of elastic forces due to surface ridges or grooves on a surface contacting the liquid crystal layer; and the .foregoing compositions, therefore, are. exem- 9 plary with the inventive approach being equally useful in alignment ofanyliquid crystals,

Processing Surfaces meeting the requirements set forth in section 2b above may be prepared by a variety of techniques. Grooves o'r ridges may be prepared by mechanical means as by use of abrasives, such as use of diamond dust or carborundum,'0r material of lesser hardness for softer substrates. They may be produced by etching or deposition. Etching may be accomplished chemically or electrochemically with or without masks. Deposition may be accomplished from a vapor or liquid state, for example, by thermal decomposition by vapor. Other techniques include ion milling, selective melting,

etc.

They may be produced by replication, always in sub- I strate compositions of the type described, from mixtures which may be produced mechanically or by other means.

Technical and Design Considerations quired for alignment in accordance with earlier techniques (thereby avoiding deleterious chemical reaction and also instability often associated with such long chain molecules). Utilizing the inventive approach, it is now possible to clean a surface before application of the liquid crystalline material and thereby avoid contamination which may also cause deterioration (earlier techniques could not tolerate a cleaning step after deposition of long chain molecules or modification of long chain molecule surfaces).

Based on theoretical development as experimentally verified, it is possible to specify the types of contour changes and spacings most useful for accomplishing the inventive result. As broad limits, it is required that any contour elevational change responsible for alignment be of a dimension of the order of a liquid crystal molecule diameter. This requires a minimum dimension of the order of about 5 angstrom units. A maximum elevational change effective for the inventive purposes is about one micrometer. For dimensions substantially exceeding this depth or height, alignment force becomes relatively weak. Both limits are of practical significance as well. Depths of less than about five angstrom .units are not practically attainable. Exceeding 'the maximum has two further implications; there are often optical disadvantages, in terms of the increased scattering, that may. result, and the thicker liquid crystal layers, required to assure continuity across the surface, give rise-to other difficulties, for example, due to the need for alignment within the liquid crystalline material spaced at a considerable distance from the aligning interface. On the same basis, preferred limits are defined from about 25 angstrom units to 5000 angstrom units (1/2 micrometer).

For optimum operation, there is an interrelationship between depth or height of grooves or ridges and spacings. lntuitively, maximization of the alignment effect occurs for minimum spacing regardless of elevational change. Such maximation in alignment is desirable where the alignment is permanent, as in a fixed polarizer as well as in the majority of devices in which realignment or disalignment for the bulk of the materials separated from the interfacial layer is sufficient to accomplish desired operation. in fact, for most devices, it is desirable to maintain the alignment of the interface parallel to grooves or ridges at all times so as to minimize the time requiredito xeassume the aligned state after switching.

A theoretical development, in which the'various factors (groove depth or ridge height and spacing) are interrelated, is set forth in Vol. 28, No. 26 Plrvsical Review Letters pp. 16834686 to appear June 26, 1972. The interrelationship may be expressed as where U, additional elastic energy density adjacent to the surface when crystal molecules are aligned across rather than parallel to the surface grooves or ridges,

K an approximate average of bend and splay elastic constants of the liquid crystal (see Vol. 25,

Discussion oft/1e Faraday Society, p. l9 (1958)),

A (average) height of ridges or depth of grooves, (average) distance between ridges or grooves, and

C small numerical constant on the order of unity (e;g., 0.2 to 2).

lt is seen from the above that. alignment energy is proportional to elevation to the second power and intensity proportional to spacing to the fourth power.

The equation was developed for the practical situation in which spacing is at least as great as elevation change (a condition which naturally occurs for all usual processing techniques). In general, operation within the broad range under conditions in which spacing does not exceed 10 times the elevation change assures at least approximate alignment. The probability of nearly perfect alignment is improved as spacing is decreased, as seen from the equation. 7

While, from a theoretical standpoint, ridge or groove configuration is significant, practical procedures'for producing such contour variations invariably result in appropriate configurations, particularly for the finer grooves or ridges which are preferred. In general, such procedures'result in groove or ridgewidths (as distinguished fromspacing) of the same order of magnitude as depth or height. This is true for mechanical scoring as well as chemical techniques and other procedures discussed.

EXAMPLE I Scoredsurfaces were produced on silicate glass microscope slides by use of diamond paste with average particle size of one micrometer imbedded in leather. Slides were rubbed unidirectionally several times in order to result in grooves of depth of approximately 500 angstrom unit's separated by approximately i000 angstrom units. The slides were cleaned first with orgahic solvent, then with chromic and sulfuric acid,

rinsed with distilled water, and followed by baking'at 500 degrees Celcius for a period of about one hour. A

was rotated between cross polarizers with a maximum extinction ratio of or greater. As compared with a direction in which the ridged surfaces of the slides and the polarizer direction defines an angular displacement of approximately 45.

EXAMPLE 2 5 Similar cells were constructed, however, utilizing fused silica in lieu of silicate glass:

Example Liquid Crystal Composition 2 para-azoxydianisole 3 MBBA 4 heptyloxyazoxybenzene 5 octyloxyazoxybenzene Extinction ratios areas reported in Example 1.

EXAMPLES 6 and 7 Whereas the above examples are utilized nematic phase material, these examples were operated at reduced temperature so that the'liquid crystal media, the

compositions utilized in examples 5 and 6, were in the smectic phase. The observed extinction ratio was somewhat less than for the nematic phase dueto a slight angular displacement as between the two permitted domains. For this smectic C phase, the overall extinction ratio was about 5:l.

What is claimed is:

1. Device comprising a layer consisting essentially of liquid crystalline material in intimate contact with at least one surface of a non-liquidcrystalline material in which device the liquid crystallinematerial is substantially aligned in a given direction substantially parallel to the interface formed between the said liquid crystalline material and the non-liquid crystalline material of- 4. Device of claim 3 in which the same means includes at least one conductive electrode having a major face substantially parallel to the said interface.

5. Device of claim 4 in which the said means includes two conductive electrodes which straddle atleast a portion of the said liquid crystalline material.

substantially linear elevational variations in the nonliquid crystalline surface which are substantially parallel to each other, in which the said elevational variations are within the range of from about five angstrom units to about l0,000 angstrom units, separated by a spacing-of from about 5 angstrom unitsto about 10,000 angstrom units, and in which the said alignmentof the said liquid crystalline material is produced primarily by the said elevational variations.

2. Device ofclaim l in which the said interface is substantially free of nomliquid crystalline molecules of a greatest dimension as long as that of the greatest dimension of the molecules of the liquid crystalline material.

JQDevice of claim 1 together with means for altering the alignment of at least a portion of the said liquid crystalline material.

6. Device of claim 5 in which the said electrodes are in intimate contact with the said liquid crystalline material.

'7. Device of claim 6 in which there is a layer of additional material intermediate at least one of the said electrodes and the said liquidcrystalline material which affects the wetting angle of the said liquid crystalline material.

8. Device of claim 7 in which the said additional layer is a surfactant which causes the said liquid crystalline material to align parallel to the said interface.

9. Device of claim 4 in which the said change in alignment results in a second aligned state.

10. Device of claim 9 in which the said second aligned state is essentially orthoganal to the said interface.

ll. Device of' claim 9 in which the second aligned state is parallel to the said interface.

12. Device of claim 3 in which there are two layers of non-liquid crystalline material both in .intimate contact with the said layer of liquid crystalline material.

13. Device of claim 4 in which the surfaces of both of the said layers'of non-liquid crystalline material contain elevational variations as described and in which the interface is formed between the said liquid crystalline material and the two layers of non-liquid crystal line material are substantially parallel.

14. Device of claim 13 in which the elevational variations of the two said surfaces are substantially parallel.

15. Device of claim 14 including at least one element which is selectively transmissive for one sense of plane polarized light.

16. Device of claim 13 in which the said elevational variations of the said two non-liquid crystalline layers are essentially non-parallel.

17. Device of claim 16 in which the said elevational variations are essentially orthoganal.

18. Device of claim l7 including at least one additional element which is selectively transmissive forone sense of plane polarized light.

g 19. Device of claim 3 in which the said means includes means for changing temperature of the said liquid crystalline material.

20. Device of claim 19 in which the second state is essentially disaligned.

21. Device of claim I in which the layer consisting .essentially of the said liquid crystalline includes a chemical species which is light-absorbent which is composed of elongated molecules and in which their major axes are aligned substantially with the major axes of the molecules of the said liquid crystalline material.

I Att-esting Officer UNITED STATES PATIENT, OFFICE CERTIFICATE OF CORRECTION Patent '2.787.11o Dated January 22, .1974

Inv n fl D. W. Berreman. S. Meiboom', D.- L. White, Kahn It 'is certified that error appears in the above-identified patent and that said Letters Patentare hereby corrected as shown below:

Column 1, line 21, change "not" to --no--. Column 2', line '21, change "increases" to "increase- Column '5, line l l, after "invention; insert andline 17, after "invention" delete "5 and" and insert a period;

line 53, delete "The remainder of the device, "5'

line 54," deletejin its entirety;

line 55, delete in its entirety;

' line 56, delete n conjunction with FIG. 1. I

Column 11, line 5, delete "As compared with a";

line '6,- delete in its entirety; line 7', delete in its entirety; line 8, delete in its entirety.

Signed and sealed this 9th day of July 1971,.

(SEAL) Attest:

MCCOY M. GIBSON,.JR. C. MARSHALL DANN- Commissioner of Patents I roan Po-wsouo-m UICOMM-DC SOHO-P" O u. VIIIIIIT nnmlo until I"! o-ludu.

, UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 2,187,110 7 Dated January 22, 1974 lnventbfls) DQ'W. Berreman, S. Meiboom, D. L. White, F. J. Kahn It is certified that error appears in the above-identified patent andvthat said Letters Patenpsre hereby corrected as shown below:

Column 1, line 21, change "not" to --no-,

Column 2, line '21, change "increases" to --increase--.

Column 5, line 1 L, after "invention; insert --and--;

"3 and" 'line 17, after "invention" delete H a and insert a period; 5

line 53, delete "The remainder of, the device, "3 "54,; delete in flits entirety; line 55, delete in its entirety; line '56, delete "in conjunction with FIG. 1.". Column 11, lines 5, delete "As compared with a line 6, delete in I its entirety;-

line v delete in its entirety; 7 line, 8, delete. in its entirety.

Signed sealed this 9th day of July. 1971 (SEAL) Attest: I

MCCOY M. GIBSONJR. 0. MARSHALL DANN Attesting Officer i Commissioner of Patents roan 90-10 (10-0) 

2. Device of claim 1 in which the said interface is substantially free of non-liquid crystalline molecules of a greatest dimension as long as that of the greatest dimension of the molecules of the liquid crystalline material.
 3. Device of claim 1 together with means for altering the alignment of at least a portion of the said liquid crystalline material.
 4. Device of claim 3 in which the same means includes at least one conductive electrode having a major face substantially parallel to the said interface.
 5. Device of claim 4 in which the said means includes two conductive electrodes which straddle at least a portion of the said liquid crystalline material.
 6. Device of claim 5 in which the said electrodes are in intimate contact with the said liquid crystalline material.
 7. Device of claim 6 in which there is a layer of additional material intermediate at least one of the said electrodes and the said liquid crystalline material which affects the wetting angle of the said liquid crystalline material.
 8. Device of claim 7 in which the said additional layer is a surfactant which causes the said liquid crystalline material to align parallel to the said interface.
 9. Device of claim 4 in which the said change in alignment results in a second aligned state.
 10. Device of claim 9 in which the said second aligned state is essentially orthoganal to the said interface.
 11. Device of claim 9 in which the second aligned state is parallel to the said interface.
 12. Device of claim 3 in which there are two layers of non-liquid crystalline material both in intimate contact with the said layer of liquid crystalline material.
 13. Device of claim 4 in which the surfaces of both of the said layers of non-liquid crystalline material contain elevational variations as described and in which the interface is formed between the said liquid crystalline material and the two layers of non-liquid crystalline material are substantially parallel.
 14. Device of claim 13 in which the elevational variations of the two said surfaces are substantially parallel.
 15. Device of claim 14 including at least one element which is selectively transmissive for one sense of plane polarized light.
 16. Device of claim 13 in which the said elevational variations of the said two non-liquid crystalline layers are essentially non-parallel.
 17. Device of claim 16 in which the said elevational variations are essentially orthoganal.
 18. Device of claim 17 including at least one additional element which is selectively transmissive for one sense of plane polarized light.
 19. Device of claim 3 in which the said means includes means for changing temperature of the said liquid crystalline material.
 20. Device of claim 19 in which the second state is essentially disaligned.
 21. Device of claim 1 in which the layer consisting essentially of the said liquid crystalline includes a chemical species which is light-absorbent which is composed of elongated molecules and in which their major axes are aligned substantially with the major axes of the molecules of the said liquid crystalline material. 